Step 1

Preheat the oven to 300°F. Line a baking sheet with parchment paper. Using a dark marker, draw a 9-inch diameter circle on the parchment paper by tracing around a 9-inch cake pan or plate. Flip the paper over so your meringue won't touch the marker.

Step 2

In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites and salt on medium speed until foamy soft peaks form, about a minute. Increase the speed to medium-high and gradually add the sugar; continue beating until stiff peaks form, 8-9 minutes. (The meringue will be glossy.)

Step 3

Pass the cocoa powder through a sieve or sifter and add to the meringue. Add the vinegar and chopped chocolate. Using a large rubber spatula, fold the mixture until well combined. It should be a light mocha color with no white or brown streaks.

Step 4

Secure the parchment paper to the baking sheet by adding a dab of meringue under each corner. Mound the meringue onto the parchment inside the circle. Using the spatula or a butter knife, spread the meringue to fill the circle. Even the top and sides just slightly -- it shouldn’t be perfectly smooth or overworked. Place in the oven and cook for 65 to 75 minutes, or until the meringue is puffed and crisp all over, yet still a bit wobbly underneath if you touch the center. Don't worry if the top is cracked -- that's normal and it all gets covered with whipped cream in the end. Turn off the oven, prop the oven door open, and leave the meringue in the oven to cool to room temperature, at least 30 minutes. (The meringue won’t collapse as much if it cools gradually.)

Step 5

Before serving, carefully peel the meringue off of the parchment paper and place it on a serving platter. In a medium bowl, beat the mascarpone cheese, heavy cream, and vanilla on medium speed until just combined. Gradually add the sugar and continue beating until it holds soft, pillowy peaks. Do not overbeat; it should not be too stiff or grainy. Mound the mascarpone cream onto the meringue and gently spread it out about 1 inch from the edge (don't worry if the meringue cracks in the process). Top the pavlova with the raspberries and sprinkle the shaved chocolate over top. Cut the pavlova into wedges, wiping the knife in between slices, and serve.

Step 6

Note: If you don't have superfine sugar, place regular granulated sugar in a food processor and pulse until fine, about 30 seconds.

Step 7

Note: This pavlova can be made ahead and assembled up to 12 hours ahead of time. Keep in the refrigerator.